Electromagnetic drive for a horological instrument



March 10, 1970 P. WUTHRICH 3,499,278

ELECTROMAGNETIC DRIVE FOR A HOROLOGICA L INSTRUMENT Filed Feb. 5. 1967 4 Sheets-Sheet 1 INVENTOR. PAUL Wl/I'HR/CH BY 1x64 ATraPA/E' 5 March 10, 1970 P. WUTH RICH 3,499,278

ELECTROMAGNETIC DRIVE FOR A HOROLOGICAL INSTRUMENT Filed Feb. 5. 1967 4 Sheets-Sheetv 2 INVENTOR. PA UL WU THRICH FIG.2 2 mw Wz% a March 10, 1970 P. WUTHRICH 3,499,278

ELECTROMAGNETIC DRIVE FOR A HOROLOGICAL INSTRUMENT Filed Feb. 5, 1967 4 Sheets-Sheet 3 ONE FULL TOOTH P/CKUP FOR 3 V/BRATOR CYCLES m4: FIG. -I3

F 4 INVENTOR.

PA UL WU THR/Cl-l ATTORNEXS" March 10, 19.70 P. wu-rH lc 3,499,278

ELECTROMAGNETIC DRIVE FOR A HOROLOGICAL INSTRUMENT Filed Feb. 5, 1967 4 Sheets-Sheet 4 /5 F IG. 7 0 xm m filb I624, x534 w; 544 we at; A656 INVENTOR. P4 UL WU THR/C H United States Patent 3,499,278 ELECTROMAGNETIC DRIVE FOR A HOROLOGICAL INSTRUMENT Paul Wuthrich, Woodbury, Conn., assignor to The United States Time Corporation, Waterbury, Conn., a corporation of Connecticut Filed Feb. 3, 1967, Ser. No. 613,902 Int. Cl. G04c 3/00 US. Cl. 5823 7 Claims ABSTRACT OF THE DISCLOSURE An electronic watch has a power source and a driven vibrator. The vibrator is attached to a magnetizable pawl. A coil around the pawl is selectively pulsed so that the pawl magnetically drives a ratchet (index) wheel. Preferably the pawl has a plurality of teeth which cooperate with the teeth of the ratchet wheel in a vernier effect.

The present invention relates to a horological instrument. More specifically, it relates to a watch in which the linear movement of a mechanical vibrator is converted into rotary movement for driving the hands.

One type of watch employing an electric battery as its power source uses an electromagnetically driven oscillator. A pawl, attached to the oscillator, acts on the teeth of a ratchet (index) wheel and causes its rotation. The ratchet wheel is connected to a conventional gear train which turns the hands of the watch.

Other types of similar mechanisms have been proposed, for example, in which two pawls attached to different arms of an oscillator mechanically act on a wheel or in which one or two pawls attached to an oscillator magnetically drive a wheel.

Various troubles and disadvantages have been encountered with the use of these types of horological devices. In the devices utilizing the physical action of a pawl on a ratchet wheel, unless special precautions are taken, the frictional resistance in the pawl and ratchet wheel device may lead to a high rate of wear. In both the magnetic and physical types a pawl stroke amplitude greater than the pitch of the ratchet wheel may cause the wheel to be advanced two teeth instead of one at every stroke of the pawl. Each stroke of the pawl must index the ratchet wheel one full unit of pitch, thus defining practical limits of the dimensions of the ratchet wheel and the frequency of pawl strokes. It is desirable, for accurate timekeeping, to operate the oscillator at a relatively high frequency. This has meant that the ratchet wheel has had to be comparatively small, fragile, and expensive.

It is the objective of the present invention to provide a horological instrument which substantially improves timepiece accuracy by the reduction of frictional resistance and which produces uniform rotational motion from reciprocating motion of varying amplitude.

It is a further objective of the invention to provide a mechanism which rotates the ratchet wheel in a horological instrument a fractional unit of the pitch of the wheel for each stroke of the pawl mechanism, thereby allowing agreater freedom in the design of timepiece movements and reducing their manufacturing cost.

In accordance with the present invention, an index (ratchet) wheel is provided which is attracted by a magnet, for example, of ferrous material. A pawl of magnetizable material is oscillated almost tangentially to the cir cumference of the index wheel. The pawl is either itself an electromagnetically driven oscillator or is attached to such an oscillator. A coil wound around the pawl magnetizes the pawl for a portion of the period of its oscil lation. Preferably the coil is pulsed with current for a time period whose length is inversely proportional to the physical amplitude. of the pawls oscillation. Preferably the teeth of the pawl are spaced wider apart than the teeth of the index wheel to provide a vernier effect. With the correct spacing of teeth, the index wheel is turned, for example, one pitch for every three complete oscillations of the magnetized pawl. The pawl attracts the wheel for about the same distance on each of its oscillations, because when its amplitude of swing is too great its period of magnetization, and of attracting the wheel, is correspondingly shortened. A permanent magnet having a plurality of projecting teeth is provided to detent the index wheel. Preferably, the spacing of the teeth of the detenting magnet is larger than the pitch of the teeth of the index wheel, so that it also obtains a vernier effect.

Other objectives of the present invention will become more fully apparent from the following detailed description read in connection with the accompanying drawings, which illustrate the preferred embodiment of the invention.

In the drawings:

FIG. 1 is a top plan view, partly exposed, showing the watch of the present invention;

FIG. 2 is an enlarged top plan view of the magnetic vernier indexing device;

FIG. 3 is a diagrammatic presentation of the relative positions of the drive magnet pole tips and index wheel teeth in the preferred embodiment during rotation of the wheel through one unit of pitch;

FIG. 4 is a chart showing the timing of the physical movement of the magnetic pawl and the timing of the pulse given to its energizing coil;

FIGS. 5, 6 7 and 9 are circuit diagrams of suitable preferred circuits for use in connection with the present invention; and

FIG. 8 is a chart showing the. functioning of the circuit of FIG. 9.

The horological instrument of the present invention is described in connection with a watch, shown in FIG. 1; however, the invention is also applicable in other horological instruments.

The watch of FIG. 1 includes a case 3 having a bezel 3a. A transparent crystal 11 is removably affixed to the case 3 and covers the dial 6 within the case. A plurality of rotatable hands 7 rotate around the dial to indicate the time. The watch is powered by a small electrical primary cell 8 within the case, although secondary cells or solar cells or other electrical power sources may also be used. The battery 8 is connected by leads 9 to a circuit 2 having a drive coil 5. The coil 5, when energized, cooperates with a permanent magnet 10, causing the oscillation of a vibrator 1. A vibrator is described and claimed in US. Patent 3,201,932 to Sparing. However, it is an objective of the present invention to enable the use of a simpler vibrator having a higher frequency. The vibrator 1 drives an index wheel 14 by means of electromagnet 13. The index wheel 14 is connected to a conventional geared dial train 12 which turns the hands 7 of the watch.

The magnetic vernier indexing drive according to the present invention is shown in FIG. 2. An electromagnet 13 is attached to the output bar of the vibrator 1. The electromagnet 13 is caused to vibrate adjacent to and in the plane of an index (ratchet) wheel 14. The wheel 14 is preferably of steel. The are of vibration of magnet 13 is relatively short in amplitude and consequently relatively flat and comes close to being a tangent to the index wheel 14. The electromagnet 13 is a combination of polarization coil 15 and a magnetizable pole piece 16. The pole piece 16 terminates in six equally spaced teeth 37, 38, 39, 4t), 41 and 42. The index wheel 14 has a number of magnetizable teeth about the circumference,

3 among which are 43, 44, 45, 46, 47, 48, 49 and 50, which are equally spaced in regard to each other. The spacing between the teeth 37-42 on pole piece 16 is slightly larger, for example, by one-third, than the spacing between the teeth (the pitch of the teeth 4350, etc.) of the index wheel 14.

In operation, the polarization coil of the electromagnet 13 is energized during a portion, preferably about one-third, of each forward oscillating stroke in the direction denoted by arrow A. The teeth 38 and 41 of the electromagnet 13 attract the teeth 45 and 49, respectively, of wheel 14, causing the wheel to rotate. Such rotation, due to the short energizing period, will be only a portion of the pitch of the index wheel, perferably one-third. During the return stroke of the vibrator 1, the polarizing coil 15 is not energized and the motion of the electromagnet 13 has no eifect on the position or motion of the index wheel 14.

The frequency of oscillation of the electromagnet 13 is maintained stable by use of the natural frequency of the vibrator 1. The amplitude of each increment of motion applied to the index wheel 14 by the electromagnet 13 is maintained constant by means of the magnetic vernier indexing mechanism and by control of the length of period that the polarization coil is energized.

When the polarization coil 15 of the electromagnet 13 is no longer energized, the major force on the index wheel is that of the detent magnet 21. Preferably, detent magnet 21 is a permanent magnet. Its direction of permanent magnetization is shown by arrows B. The detent magnet 21 has six pole tips (teeth) 70-75. Its pole tips 71 and 74, in FIG. 2, attract the nearest two index wheel teeth 77 and 81, respectively. The pole tips 70-75 are spaced further apart, by one-third, than the pitch of the teeth on index wheel 14, to provide a vernier effect. The detent magnet 21 positions the index wheel 14 until its holding force is overcome by the magnetic attraction on index wheel 14 from the moving electromagnet 13 during the next stroke.

The polarization coil 15 is activated for a small portion of each forward stroke of the vibrator 1 for the period of time necessary to rotate the index wheel 14 a distance P/ 3, where P is the pitch of the index wheel teeth. The detent magnet 21 is capable of correcting and stabilizing this unit of rotation during the interval between strokes to exactly P/ 3 from a range of P/ 3iP/ 6.

As shown in FIG. 3, the teeth 37-42 of the electromagnet13 have a vernier relationship to the teeth 43-50 of the index wheel 14. The SUB-FIGURES 3a-3h present the teeth of the electromagnet 13 in different consecutive positions relative to the teeth of the index wheel 14. One full tooth pick-up of the index wheel for three oscillations of the electromagnet is shown from 118 to 119, i.e., FIGS. 3b through 3h.

At the first position, shown at FIG. 3a, the teeth 38 and 41 of electromagnet 13 are proximate teeth 45 and 49, respectively, of the index wheel 14. The electromagnet is oscillated to the right, in FIG. 3b, carrying teeth 45 and 49, and wheel 14, in the clockwise direction. The electromagnet 13, in FIG. 3c, has returned to its initial position, i.e., its position in FIG. 3a.

However, the wheel 14, because the electromagnet is not energized during its return swing and because of the holding action of detent magnet 21, does not move backwards, i.e., counterclockwise.

The electromagnet 13, in its next forward swing, starting at the position shown in FIG. 30, picks up teeth 46 and 50, with its teeth 39 and 42, respectively. The swing carries the teeth 46 and 50 of wheel 14 clockwise to the position shown in FIG. 3d. The extreme position of the return swing of the electromagnet 13 is shown in FIG. 3e, at which position its teeth 37 and pick up teeth 43 and 47, respectively. The swing of the electromagnet brings the wheels teeth 43 and 47 clockwise to the position shown in FIG. 3 f. The next return and pick-up position is FIG. 3g, which shows teeth 38 and 41 picking up teeth 44 and 48, respectively. These teeth are moved clockwise to the position shown in FIG. 3h. A similar vernier effect occurs between the pole pieces 70 of detent magnet 21 and the teeth of the index wheel 4. The movement of the teeth 76-82 during one oscillation of the electromagnet 13 is shown by the dotted lines for the teeth in FIG. 2.

The timing of the energizing pulse to coil 15 of electromagnet 13 is shown in FIG. 4. The normal physical amplitude of the vibrator 1, and consequently of electromagnet 13, is shown in dashed lines at 51. The coil 15 is energized only during the forward stroke, at pulse times 52, 53 and 54. The normal amplitude 51 is shown as being slightly greater than the amplitude 59 to 60, which is the minimum stroke required for a positive indexing of wheel 4.

In the circuit shown in FIG. 5, the energizing coil 15 of the electromagnet 13 is connected to the collector of transistor 90. The pick-up coil 92 of the oscillator is connected to the base of pick-up transistor 91. The circuit to the drive coil 5 of the oscillator 1 which is used to impulse the oscillator 1 is a triggered blocked oscillator and is further described in connection with the detailed showing of FIG. 7 which follows. The transistor 91 is selected so that its forward current is low and its turns on (conducts) as soon as an induced voltage appears across coil 92. The transistor is tumed on later, its lag being caused by a delay network including capacitor 95 and resistance 97. When transistor 90 is turned on, it causes transistor 91 to be turned off, because of the current flow to ground through resistor 96. Transistor 90 is switched off because of the end of the induced voltage pulse in the pickup coil 92.

The output pulse of this circuit is sufficiently large in current amplitude and duration so that, even with variations in its magnitude, it will be suflicient to pulse coil 15 for a suflicient period so that electromagnet 13 indexes a tooth of the index wheel. The vernier effect, described above, makes it possible to ignore if the pulse duration to coil 15 is too long, within limits. Such long pulses do not adversely alfect the indexing of the index wheel 14 by the electromagnet 13. Physical stops on electromagnet 13 (not shown) may be used to prevent its over-long excursions.

One alternative for the electronic circuitry of the present invention is a circuit based on US. Patent 3,061,796 to Schoninger and shown in FIG. 6 herein. The circuit includes two complementary transistors, PNP transistor 107 and NPN transistor 101. The combination pick-up and control coil 102 is a single coil used for both purposes and is physically oscillated relative to a permanent magnet. The coil 102 may move relative to the fixed magnet or the magnet 10 may move and the coil be fixed, or both may oscillate simultaneously in opposite directions. A condenser 104 and a resistor 105 are connected to the base of transistor 107. The circuit also includes resistors 103, 108 and 109, which form, along with the coil 102 and 15b, a bridge network. In this circuit the width of the drive pulse is inversely proportional to the amplitude of mechanical oscillation, as is explained at col. 3, lines 1-27, of the patent. The circuit has positive feed-back in the sense that the movement of coil 102 provides a control pulse which is amplified in the sense that the coil 102 is effectively connected to the battery 81; to receive a drive pulse. The control pulse is shifted out of phase by the circuit and reproduced with a larger current to become the drive pulse to coil 102. The circuit may also utilize negative feed-back, for example, by well-known amplitude stabilization means. A suitable negative feed-back path would include a nonlinear resistance 106 in the base circuit of transistor 107, to obtain a control of the total current amplitude of the drive pulse which is inversely proportional to the physical movement of the coil 102 relative to its magnet. A suitable non-linear resistance 106 is a varistor. Coil 102 is connected in series with the coil 15, which is the control coil wound about the electromagnet 13. Using this circuit it is possible to vary the time period of the pulse to coil 15. The time period of the pulse is inverse to the physical amplitude of the swing of the electromagnet. As shown in FIG. 4, when the physical amplitude of the electromagnet 13 is excessive, as in dotted line 55, the periods of time for which the coil 15 is energized is shortened, as in the short pulses 56, 57 and 58.

Another alternative circuit is shown in FIG. 7. This circuit 110 is a triggered blocked oscillator which provides an output pulse which is constant in amplitude and duration (pulse width) in response to a triggering control pulse. The circuit 110 includes a drive coil 114 (15,000

ohms), a pick-up coil 116 (15,000 ohms), the polarization coil 15 of the electromagnet 13, battery 80 (1.6 volts) and NPN transistor 111. The emitter and collector of transistor 111 are joined by condensor 112 (.01 mid). A resistor 117 (2 meg.) and a condensor 113 (.22 mfd.) complete the circuit. The electrical values are examples of those which may be chosen to achieve the above-stated results. The magnet is shown as moving relative to the coils 114 and 116, but, as mentioned above, the coils may also move. Other suitable types of triggered blocked oscillators may be used.

In the alternative circuit of FIG. 9, the width of the drive pulse from its leading to its trailing edge is constant; however, a variable portion is taken from its center. In effect, the energy of the pulse varies inversely with the physical amplitude of the vibrator. In FIG. 8 the pulse 150 is a normal pulse and consists of a first part 150a and a second part The width of the two parts is 1500. The second pulse 1510, b is also a normal pulse. The third pulse and the fourth pulse 153a, b, 152a, b are of reduced total energy. These reduced pulses 152a, b and 153a, b are caused by an over-large amplitude swing of the vibrator. The total width 1520 of pulse 152 is the same as the width, i.e., from leading to trailing edge, of pulse 150. The next two pulses, 154a, b and 155a, b, are greater in total energy, due to the underswing of the vibrator.

In the circuit of FIG. 9 the pick-up coil 160 overcomes the normal bias of transistor 161 and turns it on. The transistor 161 may be used to trigger a Schmitt trigger circuit (not shown) to obtain the ideal squareshaped wave forms of FIG. 8. The transistor 161 is coupled to transistor 162 and overcomes its normal off bias. The drive coil 163 and the coil 15 of the electromagnet are connected in the collector circuit of transistor 162. If the induced pulse is too large, because of an over-swing of the vibrator, a large pulse is induced in coil 164. This large pulse overcomes the bias of resistor 165, causing transistor 166 to conduct and swamp the pulse from coil 160. The transistor 162 is returned to its normal off state. The drive transistor 162 is in a common-base configuration. The coils 164, 160 and 163 may be combined for greater simplicity.

It will be clear from the foregoing that the rate of rotation of the index wheel is independent of the amplitude of the vibrator over a broad range, as a result of the correction due to the Vernier indexing mechanism and due to energizing control of the polarization coil.

I claim:

1. A horological device comprising a base plate, a source of electrical current, a mechanical vibrator, means including a first coil to vibrate the said vibrator, an electromagnet attached to the said vibrator so as to oscillate with the vibrator, said electromagnet including a second coil, an index wheel rotatable by the magnetic attraction of said electromagnet, a gear train pivotally attached to the said plate and driven by the said index Wheel and means for sensing the motion of the said vibrator, said sensing means connected to and controlling the energization of said second coil from said source to energize the said electromagnet only during a portion of the oscillation period of the vibrator.

2. A horological device as set forth in claim 1, wherein said means for sensing the motion of said vibrator includes a sensing coil positioned adjacent to the said vibrator, the relative motion of said sensing coil and said vibrator generating electric current in said sensing coil, and a negative feedback amplifier connected to the said coil and controlled by it, the amplifier being connected to the said electromagnet to control the length of period of energization of said electromagnet and synchronize the energization of said electromagnet to coincide with a portion of each cycle of said vibrator.

3. A horological device as set forth in claim 1, wherein said electromagnet is provided with a plurality of pole tips and the index wheel has teeth about its circumference which are magnetically attracted by the said pole tips.

4. A horological device as set forth in claim 3, wherein the pitch of said pole tips and the pitch of said index wheel is not equal.

5. A horological device as set forth in claim 1 and also including a detent magnet attached to the said plate close to the said index wheel and having a plurality of pole tips cooperating magnetically with said index wheel teeth to stabilize said wheel during periods when said electromagnet is not energized.

6. A horological device as set forth in claim 5, wherein said detent magnet is a permanent magnet.

7. A horological device as set forth in claim 5, wherein the pitch of said electromagnet pole tips and the pitch of said detent magnet is not equal to the pitch of said index Wheel teeth.

References Cited UNITED STATES PATENTS 3,277,644 10/1966 Nomura et al 582 3 FOREIGN PATENTS 698,406 10/1953 Great Britain.

RICHARD B. WILKINSON, Primary Examiner EDITH C. SIMMONS, Assistant Examiner UB ER. 31037 

